This invention has relation to telescoping beams used as elements of hydraulic extensible crane booms, for example. Such crane booms include a plurality of hollow, telescopic boom sections or beams powered to increase and decrease the boom length by sliding with respect to each other.
In telescopic crane booms presently of commerce, forwardly mounted wear pads or slide pads are provided inside of the forward end of each inward boom section to be in supporting bearing relationship with respect to the underside of its associated outward boom section. Rearwardly mounted slide pads or wear pads are provided outside of the rear end of each outward boom section to be in bearing relationship with respect to the inner top surface of the inward boom section. These pads are provided to support the vertical reactive forces of the weight of the outward boom sections and the load being handled by the boom and also to provide sufficient surface to distribute the load in the boom sections or beams. Further, the slide pads accommodate the wear which accompanies the sliding action by being softer than the adjacent beam surface on which they slide. In such telescopic crane booms, means must also be provided to maintain lateral alignment of the boom section or beams with respect to each other. This has usually been accomplished by providing side wear pads mounted on shims, which can, with difficulty, be adjusted to compensate for wear.
Because of the fact that deflection of the boom sections or beams occurs under load, and because the pad reaction forces are very high, the wear pad or sliding pad base and the sliding boom section plate are not always parallel to each other; and as the beams slide with respect to each other and as the loading changes, this relationship of the wear pad base to the sliding boom section plate is a dynamic relationship and can change as the beams slide with respect to each other. This creates a problem in distributing the forces between adjoining boom sections or beams so as to eliminate edge loading of the wear pads. Also, because of manufacturing tolerances, the two innernested sections will not always be exactly parallel to each other. Therefore, a wear pad which can pivot with respect to the boom section to which it is mounted to conform to the surface area of the boom section on which it is sliding should be provided. Such a structure is disclosed in our co-pending application Ser. No. 948,773, filed Oct. 5, 1978 for SELF-ALIGNING FLEXIBLE SLIDE PADS FOR TELESCOPING BEAMS, now abandoned: and the complete disclosure of that application is incorporated herein by this reference to it.
Several other inherent problems associated with prior art telescoping beams such as telescopic crane booms, for example, include inefficient use of the structural material therein causing the highest stresses to be in the corners, tending to cause compressive buckling of the bottom plate, tending to cause local compressive buckling of the side plates in the front pad area, and causing problems in the lateral alignment of the sections with respect to each other.
The crane industry has attempted to solve some of these problems, with not entirely satisfactory results.
Compressive buckling of the side plate is overcome by providing stiffeners in the zone of side plate compression. Because the sections are telescopic with respect to each other, however, these stiffeners are required over a great length of the section in question, adding substantially to the weight of the boom section or beam, and thus reducing the amount of payload that can be handled by the boom.
Bent top and bottom plates have been provided to make the boom sections self-aligning, but extra care has to be taken in such structures to assure the stability of the boom against twisting and other lateral instability.
At an early stage of the development of this invention, a preliminary search was made and the following patents were located:
U.S. Pat. No. 3,708,937 granted to Sterner in January of 1973; PA1 U.S. Pat. No. 3,719,404 granted to Sterner in March of 1973; PA1 U.S. Pat. No. 3,748,807 granted to Sterner in July of 1973; PA1 U.S. Pat. No. 3,907,385 granted to Bartenstein in September of 1975; and PA1 U.S. Pat. No. 3,913,659 granted to Chatourel in October of 1975.
U.S. Pat. No. 3,708,937 to Sterner shows an inverted trapezoid cross section boom with vertical acting lower wear pads 34,34' and 34", vertically acting rear wear pads 39, front lateral guides or pads 63,63' and 63" and rear lateral guides or pads 64,64' and 64".
U.S. Pat. No. 3,719,404 also to Sterner discloses swiveled wear pads 27 which are designed to adjust themselves on spherical seats to maintain a full surface contact with the sliding boom sections with which they are in contact; but which do not have any substantial ability to absorb lateral loads.
U.S. Pat. No. 3,907,385 to Bartenstein and U.S. Pat. No. 3,913,659 to Chatourel are not in the direct art, but do show broadly canted self-centering slide bearings for machinery.
U.S. Pat. No. 3,748,807 to Sterner shows adjustable lateral guides or side wear plates including forward lateral guide pads 22 positionable under the control of adjusting screws 31 and rear lateral guide pads 34 under the control of adjusting set screws 38 for controlling the lateral positioning of the beams with respect to each other while slide pads 18 handle the vertical forces on the beams.
Applicants and those in privity with them know of no closer prior art than set out above or referred to in their above identified co-pending application; and they know of no prior art which anticipates the claims made in this application.